1. Field of the Invention
The present invention relates to a rotating member assembly and a spindle motor including the same.
2. Description of the Related Art
A hard disk drive (HDD), an information storage device, reads data stored on a disk or writes data to a disk using a read/write head.
A hard disk drive requires a disk drive device capable of driving the disk. In the disk drive device, a small-sized spindle motor is commonly used.
This small-sized spindle motor has used a hydrodynamic bearing assembly. A lubricating fluid is interposed between shaft, a rotating member of the hydrodynamic bearing assembly, and a sleeve, a fixed member thereof, such that the shaft is supported by fluid dynamic pressure generated in the lubricating fluid.
In addition, a rotor hub rotating together with the shaft and having a recording disk mounted thereon is mounted on an upper portion of the shaft. The rotor hub is fixedly coupled to the upper portion of the shaft and has a disk shape in which it is extended in a radial direction based on the shaft.
Here, the shaft may have a step, such that the rotor hub may be fittingly-coupled to an upper portion of the step in a state in which the upper portion of the shaft has a diameter larger than that of a lower portion thereof based on the step.
In addition, fixed members such as a sleeve, and the like, are provided outwardly of the shaft and a lower portion of the rotor hub to form the spindle motor.
In the spindle motor having this structure, the rotor hub has force, biased in a downward axial direction by load of the rotor hub itself and load of the disk, applied thereto. This rotor hub generates force lifting the shaft by the principle of a lever, using a fixed member such as the sleeve, or the like, as a support. However, floating of the shaft in an upward axial direction is limited by a stopper, or the like, such that the shaft has tensile force applied thereto. In the case in which the tensile force is excessive, the shaft may be shear-fractured or broken.
Further, since the rotor hub is fixed to the shaft in a state in which it is held on the step of the shaft, load may act on the step in the downward axial direction, causing a deformation in the shape of the shaft.
A coupling structure between a shaft and a hub has been disclosed in the following Related Art Document. In the coupling structure between the shaft and the hub disclosed in the following Related Art Document, a step is not formed in a coupling surface between the shaft and the hub, such that the shaft may be damaged.